In recent years, demands for a compact transformer called a low-profile transformer employed in a DC-DC converter or the like increase. Particularly, when a transformer is to be employed in a DC-DC converter used in a compact DC power supply or the like, the low-profile transformer which is compact and low in height is sought for. As is known well, a fluorescent light is usually employed as a backlight in a liquid crystal display device or the like. An inverter circuit that drives a discharge lamp such as the fluorescent light also requires a compact transformer.
Conventionally, in the manufacture of a transformer-type coil device to be incorporated in the compact transformer, a primary winding portion and secondary winding portion which form the coil device are first formed independently of each other, and then the obtained primary winding portion and secondary winding portion are overlaid to constitute the transformer-type coil device. A pair of such transformer-type coil devices are prepared and incorporated with a magnetic core, thus manufacturing a compact transformer. This is how a transformer-type coil device is normally manufactured.
In a compact, low-profile transformer employed in a DC-DC converter, an inverter used for driving a discharge lamp, or the like, one set to a plurality of sets of coil devices each comprising a primary coil and secondary coil are incorporated between an upper core portion and lower core portion to constitute the low-profile transformer.